1. Field of the Invention
The present invention relates generally to a semiconductor structure and fabrication method thereof, and more specifically, to a semiconductor structure and fabrication method thereof, which forms a metallic nitride layer between a buffer layer and a metallic oxide layer.
2. Description of the Prior Art
In modern semiconductor processes, dielectric layers having a high dielectric constant are suited for use with metal gates. Due to the material difference, such as lattice constant difference, in a dielectric layer having a high dielectric constant and a substrate (such as a silicon substrate), a buffer layer is needed to be formed between both of them for buffering, wherein the dielectric layer having a high dielectric constant is often composed of a metallic oxide layer and the buffer layer is an oxide layer. Ina semiconductor process such as a transistor process, at least a thermal annealing process is performed at different times according to processing methods. The thermal annealing process will cause the buffer layer to absorb the oxygen atoms in the metallic oxide layer formed on the buffer layer or imported during thermal annealing process, so that the thickness of the buffer layer is thickened, and the equivalent oxide thickness (EOT) of the semiconductor structure increases, thereby decreasing the electrical performance of the resulting semiconductor structure. In modern processes, the thickness of the forming buffer layer approaches the processing limitation and is not easy to be miniaturized. The thickened thickness of the buffer layer caused by the thermal annealing process will lead to a limitation of the semiconductor process, thereby retarding the miniaturization of the semiconductor components.
Therefore, a semiconductor structure and fabrication method thereof, for avoiding the thickness of the buffer layer from being thickened and the total equivalent oxide thickness (EOT) of the semiconductor structure from being increased, is needed in the industry.